A multicenter, open comparison of the effects of three doses of 5 cc/kg Exosurf (two 2.5 cc/kg aliquots) 12+_ 1 hours apart vs a minimum of three and a maximum of six doses of 5 cc/kg Exosurf Neonatal (ea. dose divided into two 2.5 cc/kg aliquots) given intratracheally over 4-day interval to extremely premature infants (BW _>500 and <_700 grams).